Lettuce is one crop we can grow here in Montana over a longer season than most vegetables. Lettuce and many greens can be direct-seeded as early as March 21, even though the soil is still cool. The minimum germination temperature for lettuce is about 35 degrees F. and 66 degrees F. is ideal. A cold frame or tunnel placed over the seedbed will warm the soil and hasten germination, especially if it is in a sunny spot. After planting, lettuce will be ready to cut in about three or four weeks. Sow lettuce in succession, every two weeks or so, to provide a continuous harvest all season. Lettuce prefers cooler weather and will turn bitter and bolt early if it is hot. In hotter weather, plant successive crops about 10 days apart to ensure a constant supply. Later, in cooler fall weather, stretch out the days a bit. Lettuce can be sown as late as October 20th. Use a poly tunnel or cold frame to protect late sowings from hard frosts. In a cold frame, lettuce can be harvested quite late in the year. A few varieties that tolerate colder weather and frosts include: ‘Merveille de Quatre Saisons’ an old French heirloom; ‘Red Oakleaf’; ‘Rouge d’Hiver’; ‘Valdor’ and ‘Valmain’.
Sow lettuce at the rate of 60 seeds per foot in a 3” wide band in rows 12” apart . Cover seed only 1/8” deep and firm gently. Full sun is the best spot for lettuce. Growing temperatures for lettuce range from 45 to 75 degrees F. with 60-65 degrees being ideal. There are types of lettuce that tolerate warm weather better than others. These varieties include: ‘Black-Seeded Simpson’; ‘Deer’s Tongue’; ‘Jericho’; and ‘Oakleaf’. Your plants will grow best in cool days with cool nights.
The best soil pH for lettuce is about 6.0-7.5. Since the plants have rather weak root systems, it is best if your soil is rich and moist. Germination time varies from 2-15 days. In the spring season, protect from cutworms with cardboard collars, or two layers of newspaper, or a layer of aluminum foil. Water regularly; keep moist but not wet. Water early in the day only, allowing leaves to dry before evening. Regular watering is excellent, but do not allow soil to become saturated for long periods. Lettuce does best with steady, even watering, especially in summer.
Pests on lettuce (besides cutworms) include: gophers, tarnished plant bugs, thrips, aphids, leaf miners, flea beetles, slugs, mites and nematodes. One way to minimize pests is by growing your crop under insect fabric stretched over row covers. Some diseases of lettuce are: early blight, verticillium wilt, mosaic, yellows and rust, but these are usually not troublesome here in Montana.
Cut lettuce early in the morning with scissors, cutting only as much as you need for a day or two. Try to keep it clean as you cut. When ready to use, wash carefully. After washing/drying make sure the leaves are not too wet when they are put into bags. Stuff the bags loosely with the lettuce. A person may add edible flowers of nasturtiums, pansies, or calendulas to a mix of greens to brighten up the look of a salad. Keep cut lettuce as cool as possible to prevent wilting (45- 55 degrees, in high humidity and out of the sun).